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- ItemIn Situ Fabrication of Freestanding Single-Atom-Thick 2D Metal/Metallene and 2D Metal/ Metallene Oxide Membranes: Recent Developments(Weinheim : Wiley-VCH, 2021) Ta, Huy Q.; Mendes, Rafael G.; Liu, Yu; Yang, Xiaoqin; Luo, Jingping; Bachmatiuk, Alicja; Gemming, Thomas; Zeng, Mengqi; Fu, Lei; Liu, Lijun; Rümmeli, Mark H.In recent years, two-dimensional (2D) materials have attracted a lot of research interest as they exhibit several fascinating properties. However, outside of 2D materials derived from van der Waals layered bulk materials only a few other such materials are realized, and it remains difficult to confirm their 2D freestanding structure. Despite that, many metals are predicted to exist as 2D systems. In this review, the authors summarize the recent progress made in the synthesis and characterization of these 2D metals, so called metallenes, and their oxide forms, metallene oxides as free standing 2D structures formed in situ through the use of transmission electron microscopy (TEM) and scanning TEM (STEM) to synthesize these materials. Two primary approaches for forming freestanding monoatomic metallic membranes are identified. In the first, graphene pores as a means to suspend the metallene or metallene oxide and in the second, electron-beam sputtering for the selective etching of metal alloys or thick complex initial materials is employed to obtain freestanding single-atom-thick 2D metal. The data show a growing number of 2D metals/metallenes and 2D metal/ metallene oxides having been confirmed and point to a bright future for further discoveries of these 2D materials.
- ItemHighly Symmetric and Extremely Compact Multiple Winding Microtubes by a Dry Rolling Mechanism(Weinheim : Wiley-VCH, 2020) Moradi, Somayeh; Naz, Ehsan Saei Ghareh; Li, Guodong; Bandari, Nooshin; Bandari, Vineeth Kumar; Zhu, Feng; Wendrock, Horst; Schmidt, Oliver G.Rolled-up nanotechnology has received significant attention to self-assemble planar nanomembranes into 3D micro and nanotubular architectures. These tubular structures have been well recognized as novel building blocks in a variety of applications ranging from microelectronics and nanophotonics to microbatteries and microrobotics. However, fabrication of multiwinding microtubes with precise control over the winding interfaces, which is crucial for many complex applications, is not easy to achieve by existing materials and technologies. Here, a dry rolling approach is introduced to tackle this challenge and create tight windings in compact and highly symmetric cylindrical microstructures. This technique exploits hydrophobicity of fluorocarbon polymers and the thermal expansion mismatch of polymers and inorganic films upon thermal treatment. Quality parameters for rolled-up microtubes, against which different fabrication technologies can be benchmarked are defined. The technique offers to fabricate long freestanding multiwinding microtubes as well as hierarchical architectures incorporating rolled-up wrinkled nanomembranes. This work presents an important step forward toward the fabrication of more complex but well-controlled microtubes for advanced high-quality device architectures. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemElectronic Doping and Enhancement of n‐Channel Polycrystalline OFET Performance through Gate Oxide Modifications with Aminosilanes(Weinheim : Wiley-VCH, 2021) Shin, Nara; Schellhammer, Karl Sebastian; Lee, Min Ho; Zessin, Jakob; Hambsch, Mike; Salleo, Alberto; Ortmann, Frank; Mannsfeld, Stefan C.B.Self-assembled monolayers (SAMs) are widely employed in organic field-effect transistors to modify the surface energy, surface roughness, film growth kinetics, and electrical surface potential of the gate oxide to control the device's operating voltage. In this study, amino-functionalized SAM molecules are compared to pure alkylsilane SAMS in terms of their impact on the electrical properties of organic field-effect transistors, using the n-type polycrystalline small molecule semiconductor material N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8). In order to understand the electronic impact of the amino groups, the effect of both the number of amino-containing functional groups and the SAM molecular length are systematically studied. Though amino-functionalized SAM materials have been studied previously, this study is, for the first time, able to shed light on the nature of the doping effect that occurs when the gate oxide is treated with polar aminosilane materials. By a comprehensive theoretical study of the interface on the molecular level, it is shown that the observed shift in the threshold voltage is caused by free charges, which are attracted to the PTCDI-C8 and are stabilized there by protonated aminosilanes. This attraction and the voltage shift can be systematically tuned by varying the length of the neutral terminal chain of the aminosilane. © 2021 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH
- ItemSelf‐Patterning of Multifunctional Heusler Membranes by Dewetting(Weinheim : Wiley-VCH, 2021) Lünser, Klara; Diestel, Anett; Nielsch, Kornelius; Fähler, SebastianNi-Mn-based Heusler alloys are an emerging class of materials which enable actuation by (magnetic) shape memory effects, magnetocaloric cooling, and thermomagnetic energy harvesting. Multifunctional materials have a particular advantage for miniaturization since their functionality is already built within the material. However, often complex microtechnological processing is required to bring these materials into shape. Here, self-organized formation of single crystalline membranes having arrays of rectangular holes with high aspect ratio is demonstrated. Dewetting avoids the need for complicated processing and allows to prepare freestanding Ni–Mn–Ga–Co membranes. These membranes are martensitic and magnetic, and their functional properties are not disturbed by self-patterning. Feature sizes of these membranes can be tailored by film thickness and heat treatment, and the tendencies can be explained with dewetting. As an outlook, the advantages of these multifunctional membranes for magnetocaloric and thermomagnetic microsystems are sketched. © 2021 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH
- ItemAdvances and Trends in Chemically Doped Graphene(Weinheim : Wiley-VCH, 2020) Ullah, Sami; Shi, Qitao; Zhou, Junhua; Yang, Xiaoqin; Ta, Huy Q.; Hasan, Maria; Ahmad, Nasir Mahmood; Fu, Lei; Bachmatiuk, Alicja; Rümmeli, Mark H.Chemically doped graphene materials are fascinating because these have different desirable attributes with possible synergy. The inert and gapless nature of graphene can be changed by adding a small number of heteroatoms to substitute carbon in the lattice. The doped material may display superior catalytic activities; durable, fast, and selective sensing; improved magnetic moments; photoresponses; and activity in chemical reactions. In the current review, recent advances are covered in chemically doped graphene. First, the different types of heteroatoms, their bonding configurations, and briefly their properties are discussed. This is followed by the description of various synthesis and analytical methods essential for assessing the characteristics of heterographene with specific focus on the selected graphene materials of different dopants (particularly, single dopants, including N, B, S, P, first three halogens, Ge, and Ga, and codopants, such as N/O), and more importantly, up-to-date applications enabled by the intentional doping. Finally, outlook and perspectives section review the existing challenges, future opportunities, and possible ways to improve the graphitic materials. The goal is to update and inspire the readers to establish novel doped graphene with valuable properties and for current and futuristic applications. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemTransparent Power-Generating Windows Based on Solar-Thermal-Electric Conversion(Weinheim : Wiley-VCH, 2021) Zhang, Qihao; Huang, Aibin; Ai, Xin; Liao, Jincheng; Song, Qingfeng; Reith, Heiko; Cao, Xun; Fang, Yueping; Schierning, Gabi; Nielsch, Kornelius; Bai, Shengqiang; Chen, LidongIntegrating transparent solar-harvesting systems into windows can provide renewable on-site energy supply without altering building aesthetics or imposing further design constraints. Transparent photovoltaics have shown great potential, but the increased transparency comes at the expense of reduced power-conversion efficiency. Here, a new technology that overcomes this limitation by combining solar-thermal-electric conversion with a material's wavelength-selective absorption is presented. A wavelength-selective film consisting of Cs0.33WO3 and resin facilitates high visible-light transmittance (up to 88%) and outstanding ultraviolet and infrared absorbance, thereby converting absorbed light into heat without sacrificing transparency. A prototype that couples the film with thermoelectric power generation produces an extraordinary output voltage of ≈4 V within an area of 0.01 m2 exposed to sunshine. Further optimization design and experimental verification demonstrate high conversion efficiency comparable to state-of-the-art transparent photovoltaics, enriching the library of on-site energy-saving and transparent power generation.
- ItemCurrent State-of-the-Art in the Interface/Surface Modification of Thermoelectric Materials(Weinheim : Wiley-VCH, 2021) He, Shiyang; Lehmann, Sebastian; Bahrami, Amin; Nielsch, KorneliusThermoelectric (TE) materials are prominent candidates for energy converting applications due to their excellent performance and reliability. Extensive efforts for improving their efficiency in single-/multi-phase composites comprising nano/micro-scale second phases are being made. The artificial decoration of second phases into the thermoelectric matrix in multi-phase composites, which is distinguished from the second-phase precipitation occurring during the thermally equilibrated synthesis of TE materials, can effectively enhance their performance. Theoretically, the interfacial manipulation of phase boundaries can be extended to a wide range of materials. High interface densities decrease thermal conductivity when nano/micro-scale grain boundaries are obtained and certain electronic structure modifications may increase the power factor of TE materials. Based on the distribution of second phases on the interface boundaries, the strategies can be divided into discontinuous and continuous interfacial modifications. The discontinuous interfacial modifications section in this review discusses five parts chosen according to their dispersion forms, including metals, oxides, semiconductors, carbonic compounds, and MXenes. Alternatively, gas- and solution-phase process techniques are adopted for realizing continuous surface changes, like the core–shell structure. This review offers a detailed analysis of the current state-of-the-art in the field, while identifying possibilities and obstacles for improving the performance of TE materials.
- ItemWaste Recycling in Thermoelectric Materials(Weinheim : Wiley-VCH, 2020) Bahrami, Amin; Schierning, Gabi; Nielsch, KorneliusThermoelectric (TE) technology enables the efficient conversion of waste heat generated in homes, transport, and industry into promptly accessible electrical energy. Such technology is thus finding increasing applications given the focus on alternative sources of energy. However, the synthesis of TE materials relies on costly and scarce elements, which are also environmentally damaging to extract. Moreover, spent TE modules lead to a waste of resources and cause severe pollution. To address these issues, many laboratory studies have explored the synthesis of TE materials using wastes and the recovery of scarce elements from spent modules, e.g., utilization of Si slurry as starting materials, development of biodegradable TE papers, and bacterial recovery and recycling of tellurium from spent TE modules. Yet, the outcomes of such work have not triggered sustainable industrial practices to the extent needed. This paper provides a systematic overview of the state of the art with a view to uncovering the opportunities and challenges for expanded application. Based on this overview, it explores a framework for synthesizing TE materials from waste sources with efficiencies comparable to those made from raw materials.
- ItemIn Situ Observations of Freestanding Single-Atom-Thick Gold Nanoribbons Suspended in Graphene(Weinheim : Wiley-VCH, 2020) Zhao, Liang; Ta, Huy Q.; Mendes, Rafael G.; Bachmatiuk, Alicja; Rummeli, Mark H.Bulk gold's attributes of relative chemical inertness, rarity, relatively low melting point and its beautiful sheen make it a prized material for humans. Recordings suggest it was the first metal employed by humans dating as far back to the late Paleolithic period ≈40 000 BC. However, at the nanoscale gold is expected to present new and exciting properties, not least in catalysis. Moreover, recent studies suggest a new family of single-atom-thick two-dimensional (2D) metals exist. This work shows single-atom-thick freestanding gold membranes and nanoribbons can form as suspended structures in graphene pores. Electron irradiation is shown to lead to changes to the graphene pores which lead to dynamic changes of the gold membranes which transition to a nanoribbon. The freestanding single-atom-thick 2D gold structures are relatively stable to electron irradiation for extended periods. The work should advance the development of 2D gold monolayers significantly. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim